1. Field of the Invention
The present invention relates to a pump for underground storage tanks and, more particularly, to an in-line DC brushless motor and fluid pump assembly for use in an underground storage tank to pump liquid into underground delivery lines for distribution through one or more dispensers.
2. Description of Related Prior Art
Gasoline dispensers used at automotive service stations dispense gasoline from an underground tank through a nozzle to be placed in the fill tube of an automobile gas tank. The underground tank includes a pump actuated by a user upon manipulation of a lever at the time of lifting the nozzle from its stored position on the gasoline dispenser. Downstream of the pump is a leak detector for sensing the presence of a fluid leak between the storage tank and the dispenser and to curtail dispensation in the event a leak is sensed.
Several decades ago, these pumps were suction pumps, such as centrifugal pumps, that were located above the storage tank. The pump drew liquid out of the storage tank through a pipe extending into the storage tank. The liquid was thereafter forced into the delivery line from the pump. A pump of this type required a check valve at the inlet of the pump to keep the pump from losing its prime during periods of inactivity. Often, the prime was lost because of a faulty check valve. Furthermore, the required suction or vacuum necessary to lift the fluid out of the storage tank often caused vapor bubbles or vaporlock to occur. In view of these problems attendant above ground suction pumps, submersible turbine pumps were developed and used with storage tanks. Such pumps are still widely used. A turbine pump includes a turbine impeller placed below a submersible electric motor. The motor and impeller are contained within a cylindrical shell connected to a vertical delivery pipe that extends to the top of the tank. The liquid passes through a discharge manifold and into the delivery line connected to the dispenser.
About 90 percent of storage tanks presently in use include a four inch pipe extending into the storage tank. This dimension limits the pump size to less than four inches in diameter and the motor is similarly limited in cross section. Because of the relative sizes of the impeller and the motor compared to the internal diameter of the pipe, the flow capacity past the motor is severely limited. Furthermore, the intake for the pump should be below the motor to place the intake as close as possible to the tank bottom and thereby permit essentially complete evacuation of the liquid from the storage tank.
Where flow capacity available through a pump and impeller mounted within a four inch pipe is inadequate, the present solution is that of installing a second pipe and associated impeller and pump. This adds significant costs for the additional equipment as well as the costs of installation. Another alternative is to install a pipe with a six inch diameter to accommodate a larger motor and pump. This solution includes significant costs of replacement for existing storage tanks.